No abstract

During the last half a century, great achievements have been made in molecular recognition in parallel with the invention of numerous synthetic receptors. However, the selective recognition of hydrophilic molecules in water remains a generally accepted challenge in supramolecular chemistry but is commonplace in nature. In an earlier Communication [J. Am. Chem. Soc.201613814550], we reported a pair of endo-functionalized molecular tubes that surprisingly prefer highly hydrophilic molecules over hydrophobic molecules of a similar size and shape. The hydrophobic effect and hydrogen bonding were proposed to be responsible, but their exact roles were not fully elucidated. In this Article, we present a thorough study on the binding behavior of these molecular tubes toward 44 hydrophilic molecules in water. Principal component analysis reveals that the binding strength is weakly correlated to the hydrophobicity, volume, surface area, and dipole moment of guests. Furthermore, molecular dynamics simulations show the hydrophobic effect through releasing the poorly hydrogen-bonded cavity water contributes to the binding of all the hydrophilic molecules, while hydrogen bonding differentiates these molecules and is thus the key to achieve a high selectivity toward certain hydrophilic molecules over other molecules with a similar size and shape. Therefore, a good guest for these molecular tubes should meet the following criteria: the hydrogen-bonding sites should be complementary, and the molecular volume should be large enough to expel all the cavity water but not too large to cause steric hindrance. This rule of thumb may also be used to design a selective receptor for certain hydrophilic molecules. Following these guidelines, a “best-fit” guest was found for the syn-configured molecular tube with a binding constant as high as 106 M–1.

We report a smart macrocycle with four interconvertible cavities, which can select the best-fit cavity for a given guest.

Anti-scaling technology is necessary in order to prevent the performance loss and blockage of heat-exchanger. In this research, a superhydrophobic CuO nanowire layer was prepared and utilized for anti-scaling process of CaCO 3 on the surface of copper.Modified with 1H,1H,2H,2H-perfluorooctyltriethoxy-silanen (FAS-17) the water contact angle on the CuO surface increased sharply from the 4.5±1° after anodization to 154±2° since the free surface energy decreased from 74.8 mJ/m 2 of hydrophilic surface to 0.2 mJ/m 2 of superhydrophobic surface. The scale inhibition performance of superhydrophobic CuO nanowires surface was confirmed since the corresponding scaling weight of deposited CaCO 3 decreased significantly from 0.6322 mg/cm 2 to 0.1607 mg/cm 2 . This attractive anti-scaling effect of modified superhydrophobic CuO nanowires surface should ascribe to the slow CaCO 3 crystal nucleation rate due to the low surface energy, low adhesion strength of CaCO 3 crystal and air film retained on the superhydrophobic surface.

Selective recognition of neutral hydrophilic molecules in water is a challenge for supramolecular chemistry but commonplace in nature. By mimicking the binding pocket of natural receptors, endo-functionalized molecular tubes are proposed to meet this challenge. We found that two molecular tubes with inwardly directed hydrogen-bond donors recognize highly hydrophilic solvent molecules in water with high selectivity. In the complexes, hydrogen bonding occurs in the deep and hydrophobic cavity. The cooperative action between hydrogen bonding and hydrophobic effects accounts for the high affinity and selectivity. The molecular receptor is fluorescent and can detect concentrations of 1,4-dioxane-a known carcinogen and persistent environmental contaminant-in water at a limit of 119 ppb. The method simplifies the analytic procedure for this highly hydrophilic molecule.

No abstract

No abstract

Abstract:As kerogen is the main organic component in shale, the adsorption capacity, diffusion and permeability of the gas in kerogen plays an important role in shale gas production. Based on the molecular model of type II kerogen, an organic nanoporous structure was established. The Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were used to study the adsorption and diffusion capacity of mixed gas systems with different mole ratios of CO 2 and CH 4 in the foregoing nanoporous structure, and gas adsorption, isosteric heats of adsorption and self-diffusion coefficient were obtained. The selective permeation of gas components in the organic pores was further studied. The results show that CO 2 and CH 4 present physical adsorption in the organic nanopores. The adsorption capacity of CO 2 is larger than that of CH 4 in organic pores, but the self-diffusion coefficient of CH 4 in mixed gas is larger than that of CO 2 . Moreover, the self-diffusion coefficient in the horizontal direction is larger than that in the vertical direction. The mixed gas pressure and mole ratio have limited effects on the isosteric heat and the self-diffusion of CH 4 and CO 2 adsorption. Regarding the analysis of mixed gas selective permeation, it is concluded that the adsorption selectivity of CO 2 is larger than that of CH 4 in the organic nanopores. The larger the CO 2 /CH 4 mole ratio, the greater the adsorption and permeation selectivity of mixed gas in shale. The permeation process is mainly controlled by adsorption rather than diffusion. These results are expected to reveal the adsorption and diffusion mechanism of gas in shale organics, which has a great significance for further research.